In a UMTS (Universal Mobile Telecommunications System) network, attempts are made to optimize features of the system, which are based on W-CDMA (Wideband Code Division Multiple Access), by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), for the purposes of improving spectral efficiency and improving the data rates. With this UMTS network, long-term evolution (LTE) is under study for the purposes of further increasing high-speed data rates, providing low delay, and so on (non-patent literature 1).
In a third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in an LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band, which ranges from 1.4 MHz to 20 MHz. Also, in the UMTS network, successor systems of the LTE system (referred to as, for example, “LTE-Advanced” or “LTE enhancement” (hereinafter referred to as “LTE-A”)) are under study for the purpose of achieving further broadbandization and increased speed.
Now, in radio communication, as uplink and downlink duplexing schemes, there are frequency division duplexing (FDD), which divides between the uplink and the downlink based on frequency, and time division duplexing (TDD), which divides between the uplink and the downlink based on time. In TDD, the same frequency is applied to uplink and downlink transmission, and, from one transmitting point, transmission is conducted separately between the uplink and the downlink based on time. Since the same frequency is used between the uplink and the downlink, each transmitting/receiving point (radio base station or user terminal) has to switch between transmission and reception.
Also, in TDD in the LTE system, DL/UL configurations to show combinations of downlink (DL) and uplink (UL) transmission ratios in a radio frame (formed with ten subframes) are defined (see FIG. 1). For example, FIG. 1 shows a plurality of DL/UL configurations 0 to 6, between which the ratios of DL subframes and UL subframes vary. In the LTE system, interference between uplink signals and downlink signals of neighboring transmitting/receiving points is prevented by applying the same DL/UL configuration between neighboring transmitting/receiving points.